Emission of Thermally Activated Electrons from Rare Gas Clusters Irradiated with Intense VUV Light Pulses from a Free Electron Laser

摘要

The ionization dynamics of Ar and Xe clusters irradiated with intense vacuum ultraviolet light from a free-electron laser is investigated using photoelectron spectroscopy. Clusters comprising between 70 and 900 atoms were irradiated with femtosecond pulses at 95 nm wavelength (～13 eV photon energy) and a peak intensity of ～4 x 10~(12) W/cm~2. A broad thermal distribution of emitted electrons from clusters with a maximum kinetic energy up to 30-40 eV is observed. The observation of relatively low-energy photoelectrons is in good agreement with calculations using a time-dependent Thomas-Fermi model and gives experimental evidence of an outer ionization process of the clusters, due to delayed thermo-electronic emission.